In the field of data communications, there are many types of networks that facilitate the transfer of data from one location to another. Some exemplary standards include Ethernet, E.25, Frame Relay, and Asynchronous Transfer Mode. Generally these standards are available from standards bodies such as the Institute of Electrical and Electronics Engineers (IEEE) and other organizations. The standards generally describe how the data is to be packaged and then transported across the particular network and also provide for error checking and other aspects of data transmission as they relate to the particular standard in question.
With particular focus to Ethernet networks, the standards that guide the creation and operation thereof include the IEEE Std 802.3-1995, the entire text of which is incorporated herein by reference. The IEEE Std 802.3-1995 generally discusses Ethernet networks as they relate to the Data Link and Physical layers of the International Organization for Standardization Open Systems Interconnection (ISO/OSI) Reference Model which is well known by those skilled in the art.
In the Physical and Data Link layers, the IEEE Std 802.3-1995 particularly discusses the specifications and operation of the Media Access Control (MAC) of the Data Link layer and the physical layer devices (PHYs) of the Physical layer. Also, the particular interconnection between the media access controllers and the physical layer devices is discussed, referred to as a Media Independent Interface (MII). As discussed in IEEE Std 802.3-1995, the MII may assume one of three following forms, including an integrated circuit to integrated circuit interface with traces on a printed circuit board, a motherboard to daughterboard interface between two or more circuit boards, or an interface between two printed circuit assemblies that are attached with a length of cable and an appropriate connector.
The data transfer accomplished with the MIII as specified by IEEE Std 802.3-1995 provides for bi-directional data transfer. In each direction, the MII specifies a four bit bundle of conductors to transfer four bits of data or a single nibble in a four bit parallel data transfer. Also, the MII includes a transmit enable (TX_EN) conductor in each direction that provides a pathway for a TX_EN signal indicating that the nibbles are being presented on the MII for transmission. The IEEE Std 802.3-1995 also specifies that a single MII is to be employed between a media access controller and a respective physical layer device with which the media access controller communicates. Unfortunately, this requires a number of input and output pins to accommodate the MII interface between each media access controller and its associated physical layer device given that a single chip includes a number of media access controllers. This results in a significant number of pins that places a limit on the number of media access controllers within a specific integrated circuit due to size limitations as well as resulting in real estate problems on the integrated circuit itself.